CACHE — Instruction/data cache

The cache is two-way set associative with a least recently used (LRU) replacement policy. Both instruction and data accesses towards flash memory or XIP code regions are cached.

The cache has the following features:

128-bit cache line
Configurable as a cache or general purpose RAM
Hit/miss counters per NVM region and access type (instruction or data)
Readable cache content (for profiling)
- Data, tag, valid, and most recently used (MRU) bits
- Can be disabled when not in use
Manual invalidation and erase support
Locking cache updates on cache misses

Figure 1. Cache overview

In Cache mode (MODE=Cache), instruction and data accesses from the CPU over the code bus towards internal or external flash, are cached. The contents of the cache, i.e. data, tag, valid, and MRU bits, are memory mapped, see Cache content. This can be used for performance profiling of code running in the system. Access to the cache content region is read-only by default, but can be blocked by enabling a lock bit in DEBUGLOCK. Preventing cache content updates on cache misses can be enabled through register DEBUGLOCK. When enabled, cache content is not replaced, but kept intact. The cache is still enabled and provides fast instruction and data fetches for cached content.

Access to internal or external flash memory will not be cached when in Ram mode (MODE=Ram). Instead, the cache data content, as described in Cache content, can be used as read/write RAM.

Cache content

Cache information is divided into cache info content and cache data content.

Cache info content is organized in memory as shown in the following figure.

Figure 2. Cache info content

The V field contains the bit that indicates if a cache entry is valid or not. All V fields are cleared when invalidating the cache using register INVALIDATE, when disabling the cache using register ENABLE, or when changing MODE from Ram to Cache. The MRU field indicates which way was used most recently in the set. The MRU bit is updated on each fetch from the cache and is used for the cache replacement policy. The Tag field is used to check if an entry in the cache matches the address being fetched.

The following figure shows how the cache data content is organized in memory.

Figure 3. Cache data content

Each set consists of two ways, each containing 128 bits of data. The 128-bit data is available as 4x32-bit words in sequential order. When operating in Ram mode (MODE = Ram), the data is accessible as general purpose RAM.

The cache info and cache data content are memory mapped in the CACHEINFO and CACHEDATA regions. These can be accessed in the CACHEINFO registers and CACHEDATA registers respectively.

Profiling

The cache includes profiling counters IHIT, IMISS, DHIT, and DMISS for both flash and execute-in-place (XIP).

Cache performance on executed code is indicated by these counters when enabled through PROFILINGENABLE. The counters can be cleared at any time using PROFILINGCLEAR. Writing to this register will clear all profiling counters. After being cleared, the counters will increment at the next instruction, or data fetch, according to the rules in the following table.

Table 1. Profiling counters
Profiling counter	Description
IHIT	Increased on a cache hit for instruction fetch
IMISS	Increased on a cache miss for instruction fetch
DHIT	Increased on a cache hit for data fetch (i.e. LOAD type instruction targeting the cache region)
DMISS	Increased on a cache miss for data fetch (i.e. LOAD type instruction targeting the cache region)

Registers

Table 2. Instances
Base address	Domain	Peripheral	Instance	Secure mapping	DMA security	Description	Configuration
0x50001000	APPLICATION	CACHE	CACHE	S	NA	Cache

Table 3. Register overview
Register	Offset	Description
PROFILING[n].IHIT	0x400	Instruction fetch cache hit counter for cache region n, where n=0 means Flash and n=1 means XIP.
PROFILING[n].IMISS	0x404	Instruction fetch cache miss counter for cache region n, where n=0 means Flash and n=1 means XIP.
PROFILING[n].DHIT	0x408	Data fetch cache hit counter for cache region n, where n=0 means Flash and n=1 means XIP.
PROFILING[n].DMISS	0x40C	Data fetch cache miss counter for cache region n, where n=0 means Flash and n=1 means XIP.
ENABLE	0x500	Enable cache.
INVALIDATE	0x504	Invalidate the cache.
ERASE	0x508	Erase the cache.
PROFILINGENABLE	0x50C	Enable the profiling counters.
PROFILINGCLEAR	0x510	Clear the profiling counters.
MODE	0x514	Cache mode. Switching from Cache to Ram mode causes the RAM to be cleared. Switching from RAM to Cache mode causes the cache to be invalidated.
DEBUGLOCK	0x518	Lock debug mode.
ERASESTATUS	0x51C	Cache erase status.
WRITELOCK	0x520	Lock cache updates. Prevents updating of cache content on cache misses, but will continue to lookup instruction/data fetches in content already present in the cache. Ignored in RAM mode.

PROFILING[n].IHIT (n=0..1)

Address offset: 0x400 + (n × 0x20)

Instruction fetch cache hit counter for cache region n, where n=0 means Flash and n=1 means XIP.

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID				A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	R	HITS										Number of instruction cache hits

PROFILING[n].IMISS (n=0..1)

Address offset: 0x404 + (n × 0x20)

Instruction fetch cache miss counter for cache region n, where n=0 means Flash and n=1 means XIP.

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID				A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	R	MISSES										Number of instruction cache misses

PROFILING[n].DHIT (n=0..1)

Address offset: 0x408 + (n × 0x20)

Data fetch cache hit counter for cache region n, where n=0 means Flash and n=1 means XIP.

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID				A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	R	HITS										Number of data cache hits

PROFILING[n].DMISS (n=0..1)

Address offset: 0x40C + (n × 0x20)

Data fetch cache miss counter for cache region n, where n=0 means Flash and n=1 means XIP.

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID				A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	R	MISSES										Number of data cache misses

ENABLE

Address offset: 0x500

Enable cache.

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																																			A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	RW	ENABLE										Enable cache
			Disabled	0								Disable cache
			Enabled	1								Enable cache

INVALIDATE

Address offset: 0x504

Invalidate the cache.

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																																			A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	W	INVALIDATE										Invalidate the cache
			Invalidate	1								Invalidate the cache

ERASE

Address offset: 0x508

Erase the cache.

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																																			A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	W	ERASE										Erase the cache
			Erase	1								Erase cache

PROFILINGENABLE

Address offset: 0x50C

Enable the profiling counters.

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																																			A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	RW	ENABLE										Enable the profiling counters
			Disable	0								Disable profiling
			Enable	1								Enable profiling

PROFILINGCLEAR

Address offset: 0x510

Clear the profiling counters.

The profiling counters can be cleared at any time. When cleared, all profiling counters will be set to zero, and will increment at the next instruction or data fetch.

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																																			A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	W	CLEAR										Clearing the profiling counters
			Clear	1								Clear the profiling counters

MODE

Address offset: 0x514

Cache mode.

Switching from Cache to Ram mode causes the RAM to be cleared.

Switching from RAM to Cache mode causes the cache to be invalidated.

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																																			A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	RW	MODE										Cache mode
			Cache	0								Cache mode
			Ram	1								RAM mode

DEBUGLOCK

Address offset: 0x518

Lock debug mode.

This register is ignored when CACHE is used in RAM mode. Once this register has been set to Locked, the debug mode can only be unlocked by resetting the device.

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																																			A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	RW1	DEBUGLOCK										Lock debug mode
			Unlocked	0								Debug mode unlocked
			Locked	1								Debug mode locked

ERASESTATUS

Address offset: 0x51C

Cache erase status.

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																																			A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	RW	ERASESTATUS										Cache erase status
			Idle	0								Erase is not complete or hasn't started
			Finished	1								Cache erase is finished Write 0 to clear.

WRITELOCK

Address offset: 0x520

Lock cache updates. Prevents updating of cache content on cache misses, but will continue to lookup instruction/data fetches in content already present in the cache.

Ignored in RAM mode.

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID																																			A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	RW	WRITELOCK										Lock cache updates
			Unlocked	0								Cache updates unlocked
			Locked	1								Cache updates locked

Electrical specification

Cache size

Symbol	Description				Min.	Typ.	Max.	Units
Size_CACHEDATA	CACHEDATA size					8192		Bytes

Registers

Table 4. Instances
Base address	Domain	Peripheral	Instance	Secure mapping	DMA security	Description	Configuration
0x00F08000	APPLICATION	CACHEINFO	CACHEINFO	S	NA	Cache info

Table 5. Register overview
Register	Offset	Security	Description
SET[n].WAY[o]	0x0		Cache information for SET[n], WAY[o].

SET[n].WAY[o] (n=0..255) (o=0..1)

Address offset: 0x0 + (n × 0x8) + (o × 0x4)

Cache information for SET[n], WAY[o].

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID				C	B														A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	RW	TAG										Cache tag.
B	R	V										Valid bit
			Invalid	0								Invalid cache line
			Valid	1								Valid cache line
C	R	MRU										Most recently used way.
			Way0	0								Way0 was most recently used
			Way1	1								Way1 was most recently used

Registers

Table 6. Instances
Base address	Domain	Peripheral	Instance	Secure mapping	DMA security	Description	Configuration
0x00F00000	APPLICATION	CACHEDATA	CACHEDATA	S	NA	Cache data

Table 7. Register overview
Register	Offset	Description
SET[n].WAY[o].DATA0	0x0	Cache data bits [31:0] of SET[n], WAY[o].
SET[n].WAY[o].DATA1	0x4	Cache data bits [63:32] of SET[n], WAY[o].
SET[n].WAY[o].DATA2	0x8	Cache data bits [95:64] of SET[n], WAY[o].
SET[n].WAY[o].DATA3	0xC	Cache data bits [127:96] of SET[n], WAY[o].

SET[n].WAY[o].DATA0 (n=0..255) (o=0..1)

Address offset: 0x0 + (n × 0x20) + (o × 0x10)

Cache data bits [31:0] of SET[n], WAY[o].

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID				A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	RW	Data										Data

SET[n].WAY[o].DATA1 (n=0..255) (o=0..1)

Address offset: 0x4 + (n × 0x20) + (o × 0x10)

Cache data bits [63:32] of SET[n], WAY[o].

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID				A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	RW	Data										Data

SET[n].WAY[o].DATA2 (n=0..255) (o=0..1)

Address offset: 0x8 + (n × 0x20) + (o × 0x10)

Cache data bits [95:64] of SET[n], WAY[o].

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID				A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	RW	Data										Data

SET[n].WAY[o].DATA3 (n=0..255) (o=0..1)

Address offset: 0xC + (n × 0x20) + (o × 0x10)

Cache data bits [127:96] of SET[n], WAY[o].

Bit number				31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
ID				A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A	A
Reset 0x00000000				0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
ID	R/W	Field	Value ID	Value								Description
A	RW	Data										Data